1. Field
A liquid crystal display (LCD) device and a method fabricating the same is provided.
2. Related Art
Flat panel display (FPD) devices that have high portability and low power consumption have been the subject of recent research and development. Among various types of FPD devices, liquid crystal display (LCD) devices are commonly used as monitors for notebook and desktop computers because of their ability to display high-resolution images, wide ranges of different colors, and moving images.
Generally, the LCD device includes a color filter substrate and an array substrate separated from each other by a liquid crystal layer interposed between the two substrates. The color filter substrate and the array substrate include a common electrode and a pixel electrode, respectively. When a voltage is supplied to the common electrode and the pixel electrode, an electric field is generated that changes the orientation of liquid crystal molecules of the liquid crystal layer due to optical anisotropy within the liquid crystal layer. Light transmittance characteristics of the liquid crystal layer are modulated and images are displayed by the LCD device.
Active matrix type display devices are commonly used because of their superiority in displaying moving images. Active matrix-type display devices include pixel regions disposed in a matrix form where a thin film transistor (TFT) is formed in the pixel region as a switching element. While forming the TFT, hydrogenated amorphous silicon (a-Si:H) is selected to be deposited over a large area of substrate. Hydrogenated amorphous silicon yields higher productivity while easily fabricated on the large area of the substrate. The hydrogenated amorphous silicon (a-Si:H) is deposited at a relatively low temperature, in which a glass substrate of low cost can be used. The hydrogenated amorphous silicon is used mainly in the TFT, which is referred to as an amorphous silicon thin film transistor (a-Si TFT).
Because the hydrogenated amorphous silicon has a disordered atomic arrangement, weak silicon-silicon (Si—Si) bonds and dangling bonds exist in the hydrogenated amorphous silicon. These types of bonds become metastable when light or an electric field is applied to the hydrogenated amorphous silicon. This metastability makes the TFT unstable. Electrical characteristics of the hydrogenated amorphous silicon are especially degraded due to light irradiation. A TFT that uses the hydrogenated amorphous silicon is difficult to implement in a driving circuit due to degraded electric characteristics such as a relatively low field effect mobility and a poor reliability.
To solve these problems, a polycrystalline silicon thin film transistor (p-Si TFT) is suggested. Due to the higher field effect mobility of a p-Si TFT compared to a a-Si TFT, fabrication of a driving circuit and a switching element can be achieved simultaneously. The production cost is reduced and a driving circuit is simply fabricated on a substrate where a switching element is formed.
FIG. 1 is a schematic view that shows an LCD device according to the related art where a switching element and a driving circuit are formed on a single substrate. In FIG. 1, a display area D1 and a non-display area D2 in a periphery of the display area D1 are defined on a single substrate 10. The display area D1 is disposed at a central portion of the substrate 10, while the non-display area D2 is disposed at left and top portions of the display area D1. The non-display area D2 includes a gate driving circuit 16 and a data driving circuit 18. The display area D1 includes a plurality of gate lines 12 connected to the gate driving circuit 16 and a plurality of data lines 14 connected to the data driving circuit 18. The gate line 12 and the data line 14 intersect each other to define a pixel region P. A pixel electrode 17 is formed in the pixel region P. A thin film transistor (TFT) Ts formed as a switching element is connected to the pixel electrode 17. The gate driving circuit 16 supplies a scan signal to the TFT Ts through the gate line 12 and the data driving circuit 18 supplies a data signal to the pixel electrode 17 through the data line 14.
The gate driving circuit 16 and the data driving circuit 18 are connected to an input terminal (not shown) to receive external signals (not shown). The gate driving circuit 16 and the data driving circuit 18 process the external signals from the input terminal to generate the scan signal and the data signal. To generate the scan signal and the data signal, the gate driving circuit 16 and the data driving circuit 18 include a plurality of TFTs that form complementary metal-oxide-semiconductor (CMOS) elements. For example, an inverter that includes negative (n)-type and positive (p)-type TFTs may be formed in the gate driving circuit 16 and the data driving circuit 18.
FIG. 2 is a schematic plane view that shows a display area of an LCD device according to the related art.
In FIG. 2, a gate line GL and a data line DL cross each other to define a pixel region P. A thin film transistor Ts is connected to the gate line GL and the data line DL. A pixel electrode 80, which is disposed in the pixel region P, is connected to the thin film transistor Ts. A storage capacitor Cst is disposed to be adjacent to the thin film transistor Ts in the pixel region P
Typically, the pixel electrode 80 is spaced apart from the gate and the data lines GL and DL with a predetermined distance. When the pixel electrode 80 is overlapped with the gate line GL and the data line DL, cross-talk that deteriorates an image quality occurs. The pixel electrode 80 is formed to be spaced from the gate and the data lines GL and DL. Shield spaces SP are between the gate line GL and the pixel electrode 80 and between the data line DL and the pixel electrode 80. A black matrix 52 should be formed to overlap with the space SP. The black matrix 52 is formed to overlap with regions of the thin film transistor Ts and the storage capacitor Cst as well as the space SP.
FIG. 3 is a schematic cross-sectional view showing a driving circuit of an LCD according to the related art where a switching element and a driving circuit are formed on a single substrate. FIG. 4 is a schematic cross-sectional view taken along a line IV-IV of FIG. 2.
As shown in FIGS. 3 and 4, an LCD device includes a display area D1 and a non-display area D2. The display area D1 includes a pixel region P that includes a thin film transistor region TsA and a storage capacitor region CstA.
The LCD includes a first substrate 30, a second substrate 50 that faces the first substrate 30 and a liquid crystal layer 40 between the first and the second substrate 30 and 50 in the display area D1. A black matrix 52, which is disposed in the display area D1 and the non-display area D2, is disposed on an inner surface of the second substrate 50 and a color filter layer 54, which is disposed in the display area D1, on the black matrix 52, and a common electrode 56, which is disposed in the display area D1, is formed on the color filter layer 54. Although not shown, the color filter layer 54 includes red, green and blue sub-color filter layers (not shown) that are repeatedly arranged in that order. The black matrix 52 is overlapped with regions of the gate line GL, the data line DL and spaces SP between the gate line GL and the pixel electrode 80 and between the data line DL and the pixel electrode 80.
An align margin α should be considered before attaching the first and the second substrates 30 and 50 because light leakage may occur even if the black matrix 52 is formed in the mentioned regions due to an align error. Therefore, an image quality of the LCD device is deteriorated due to light leakage.
The black matrix 52 according to the related art should be manufactured with at least 5 micrometers (μm) as the align margin α. Therefore, although the light leakage is solved from the LCD, an aperture ratio is deteriorated concerning the align margin.